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Abstract

We report direct observations of Rabi oscillations and self-induced transparency in a quantum dot optical amplifier operating at room temperature. The experiments make use of pulses whose durations are shorter than the coherence time which are characterized using Cross-Frequency-Resolved Optical Gating. A numerical model which solves the Maxwell and Schrödinger equations and accounts for the inhomogeneously broadened nature of the quantum dot gain medium confirms the experimental results. The model is also used to explain the relationship between the observability of Rabi oscillations, the pulse duration and the homogeneous and inhomogeneous spectral widths of the semiconductor.

Normalized amplitude (upper plot) and instantaneous frequency (lower plot) profiles of the pulses at the output of the SOA biased in the gain regime at 250 mA, for various input energies. Pulses are centered at 1530 nm. The different traces are separated for clarity.

Amplitude (upper plot) and instantaneous frequency (lower plot) profiles of the pulses at the output of the SOA biased in the gain regime at 150 mA, for various input energies. Pulses are centered at 1530 nm. The different traces are separated for clarity.

Normalized amplitude (upper plot) and instantaneous frequency (lower plot) profiles of the pulses at the output of the SOA biased in the absorption regime at 60 mA, for various input energies. Pulses are centered at 1530 nm. The different traces are separated for clarity.

(a) A schematic description of the distribution of homogeneous resonant transitions, which construct a Gaussian shaped inhomogeneously broadened gain spectrum. The spectrum of a short electromagnetic pulse is also illustrated. (b) An ensemble of two-level systems having different transition energies placed within a heterostructure through which the carriers are injected. Gray arrows represent resonant transitions while black arrows describe some of the incoherent relaxations.

(a) Calculated spectral profile of population inversion for the entire spectrum of accounted two-level systems, along the interaction with a 150 fs pulse. (b) The same, interacting with a 500 fs pulse. Initial conditions are of population inversion (red shades). Blue shades represent negative population inversion.